A remodeler encountering a layer of Cabot's Quilt inside an old building might mistake it for the tattered remnants of a Hawaiian grass skirt - hastily stuffed into a wall, perhaps, during a police raid of some Prohibition-era costume party. The reality is only slightly less surprising: It's an early insulating material made from dried eelgrass (a marine plant harvested from beaches in the northeastern U.S. and adjacent Canada) stitched between sheets of heavy paper. Beginning in about 1900, it was distributed nationally and heavily advertised in trade publications by its manufacturer, Boston-based Samuel Cabot Co. Today, with precious few carpenters familiar with its use still out in the field, it's less a building material than a puzzling archeological relic.
In its day, though, it was a modern marvel. Advertisements for Cabot's Quilt claimed that it would not "rot or become foul" and had the ability to "break up and absorb sound waves," to say nothing of holding heat "better than 40 layers of common building paper or 3 inches of board or 12 inches of brickwork." Arctic explorer Donald McMillan was quoted as saying that the continuous layer of the eelgrass product on the outside of his winter quarters in northern Greenland meant that "we have never been too cold, but many times too warm and obliged to throw open the doors."
McMillan's endorsement didn't mention the heat source he had in his dwelling or how much fuel it used. Both, however, must have had a lot to do with his comfort level that winter. By modern standards, the insulating value of Cabot's Quilt would have been minimal: The company's heaviest three-ply product was a nominal 2„3 inch thick -and because many builders of the day had only a shaky understanding of how insulation was supposed to work, its installed thickness was often a fraction of that. Even though the manufacturer pointed out that "it is preferable to apply [Cabot's Quilt] between studs and rafters inside a house, rather than directly under shingles, slate, or clapboards," the material is often found sandwiched tightly between layers of solid material - a condition in which it would have functioned more like heavy-duty building paper than insulation.
But even as Cabot's Quilt was reaching the peak of its popularity, larger forces were already in motion. In the 1920s, a plant disease - then identified simply as "eelgrass blight," but now known to be caused by the marine slime mold Labyrinthula zosterae - began wiping out underwater eelgrass beds. By the mid-1930s, the plant was virtually extinct across most of its range, and Cabot's Quilt soon followed it into oblivion. But sometimes, late at night when it's quiet, you can still hear the faint sound of the sea in the walls of an old house. - Jon Vara